Vascular grafts of sythetic fiber are now widely used, a variety of constructions and a variety of materials being available. A principal factor in selection of a particular graft is the porosity of the fabric of which the graft is composed. This factor is significant because the porosity controls both the tendency to hemmorrhage and the ingrowth of tissue into the wall of the graft.
The general procedure for implantation of a graft includes the step of preclotting, a step in which the graft is immersed in the blood of the patient after which the graft is allowed to stand for a period long enough for clotting to ensure. As a result, when the graft is implanted surgically, hemmorrhaging does not occur; yet, growth of tissue into the wall of the graft can proceed. This growth is extremely important, since, eventually, the wall of the graft simulates the wall of the vessel which it replaces and, if all goes properly, provides a lumen which remains open and free of clots.
The degree of adhesion of tissue to the wall of the graft varies with the material used. Thus, V. J. Lombardi in U.S. Pat. No. 3,561,441 discloses the use of a non-sticking material having loops thereon for use in covering and treating wounds. The material which he proposes to use is a polyfluorinated polyolefin filament, spun on a plastic ribbon form. Lombardi discloses that, as a result of the non-stick property, the fabric can be removed from a wound periodically as a step in the changing of the dressing without tearing open the wound itself. Obviously, such a material is not suitable for use where the material is to remain within the body.
L. R. Sauvage in U.S. Pat. No. 3,878,565 has disclosed a tubular textile synthetic cardio-vascular prothesis of polyester or other synthetic fiber, the prothesis consisting of a body having a multiplicity of fiber loops extending outwardly from the surface thereof. Also, as shown in his FIG. 2A, the body is crimped into irregular, circumferential corrugations. Such corregations are intended to provide protection against kinking or collapse of the tubing and narrowing of the lumen thereof as a result of bending or other factors. However, the degree of protection afforded by such irregular corrugation varies over the lengths of the tube and can be below the required level of protection at specific regions.
While the construction of Sauvage facilitates growth of tissue exterior to the body or trellis of the tubular graft, the absence of loops on the interior of the tubing may result in exposure of the synthetic filaments of which the tubing is composed. Furthermore, the Sauvage graft is circularly-knit so that the technique which provides the fabric loops in the Sauvage graft is not applicable to woven tubing.
Liebig et al in U.S. Pat. No. 4,047,252 have described a synthetic vascular graft which is warp-knit from a fiber or filament to which growing tissue can adhere. The preferred fiber is stated to be polyester, and an especially preferred fiber is that sold under the trade name of Dacron by Dupont. As is well known, Dacron is polyethylene terephthalate. The Liebig et al fabric, while presenting an excellent substrate for ingrowth of tissue is sufficiently porous so that preclotting is generally necessary in the use of this material. Woven fabrics, in general, have lower porosities than do knit fabrics, whether warp-knit or circularly knit, but do not present so suitable a structure for tissue ingrowth. Thus, while woven fabrics of very low porosity are available, they are not so suitable for tissue ingrowth as are the double velours, namely, those having velour loops on both the inner and outer surfaces of the fabric.
As is evident, it would be desirable that graft fabric whether tubular or flat, have low porosity and facilitate the growth of tissue along both the interior and exterior surfaces thereof.